Angiotensin converting enzyme (to be referred to as ACE hereinafter) is a kind of carboxypeptidase exists in the animal body and produces angiotensin II by digesting one of the peptide bonds of angiotensin I. The angiotensin II is a peptide hormone having a strong vasopressor activity and causes hypertension through vasoconstriction, acceleration of aldosterone secretion and the like. Accordingly, inhibition of the ACE activity makes control of angiotensin II production and treatment of hypertension possible. Up to this time, medicaments such as captopril and the like have been put into practical use and broadly used as ACE inhibitors. However, since these medicaments have strong actions, there is a possibility of causing side effects and it is necessary to pay attention to side effects such as dry cough and the like in the case of many ACE inhibitors.
On the other hand, since the angiotensin I as the substrate of ACE is a peptide, studies have been carried out on the provision of a hypertension treating agent which competitively inhibits ACE by peptides derived from a natural source and shows no side effects (e.g., see Patent References 1 to 5). Since these peptides have mild actions, high safety is expected. On the other hand, there is a problem in that a peptide or a composition containing the peptide must be ingested in a relatively large amount in order to ingest its effective amount. Additionally, since many of these peptides have the whole hydrophobic property and it is considered that such peptides generally have strong bitterness (e.g., see Patent Reference 6, Non-patent References 1 and 2), there is also a problem of having a difficulty in orally taking them in a large amount.    Patent Reference 1: JP-A-4-091097    Patent Reference 2: JP-A-5-262790    Patent Reference 3: JP-A-6-040944    Patent Reference 4: JP-A-7-188282    Patent Reference 5: JP-A-10-175997    Patent Reference 6: JP-A-2006-75064    Non-patent Reference 1: Wenyi Wang et al., Comprehensive Reviews in Food Science and Food Safety, 2005, (4), p. 63-78    Non-patent Reference 2: “Kaitei Shinpan Shokuhin Kagaku (Revised New Edition Food Chemistry)” edited by Masao Fujimaki et al., Asakura Shoten, March, 1976, p. 117-118